[PATCH] [PATCH] comedi: check for NULL get_valid_routes function pointer

[Prabhakar Pujeri <prabhakar.pujeri@gmail.com>]

From: Super User <root@localhost.localdomain>

The function get_valid_routes() calls the low-level driver's
dev->get_valid_routes() callback directly without checking if it is
set. If this function pointer is NULL, the kernel crashes with a
NULL instruction pointer dereference.

This patch adds a check to ensure the callback is present before
calling it, and returns -EINVAL if it is missing.

This prevents a kernel crash when user space invokes an ioctl that
results in get_valid_routes() being called on drivers that do not
implement the callback.

Reported-by: syzbot+ab8008c24e84adee93ff@syzkaller.appspotmail.com
Signed-off-by: Prabhakar Pujeri <prabhakar.pujeri@gmail.com>
---
 drivers/comedi/comedi_fops.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
index 3383a7ce27ff..2b8cb280287b 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -1302,6 +1302,11 @@ static int check_insn_device_config_length(struct comedi_insn *insn,
 static int get_valid_routes(struct comedi_device *dev, unsigned int *data)
 {
 	lockdep_assert_held(&dev->mutex);
+	if (!dev->get_valid_routes) {
+		dev_warn(dev->class_dev ?: dev->hw_dev,
+				"get_valid_routes() not implemented\n");
+		return -EINVAL;
+	}
 	data[1] = dev->get_valid_routes(dev, data[1], data + 2);
 	return 0;
 }
-- 
2.50.1